Liquid-vapor Growth of Atomically Thin Metal Tellurides with Controllable Polymorphism

Atomically thin transition metal dichalcogenides (TMDs), together with their polymorphism, provide promising alternatives for next generation electronic devices and a platform to explore exotic quantum phenomena. However, a large-scale synthesis method that can reliably produce high-quality two-dimensional (2D) TMDs with controlled phase is still lacking. Instead, TMDs with high concentration of defects and defect-stabilized metastable crystalline phases are often obtained via conventional chemical vapor deposition. Here we developed a liquid-vapor (LV) technique to exploit liquid precursors to significantly suppress the equilibrium shift to the decomposition direction and successfully synthesized high-quality TMDs. We highlight the importance of exploiting the synergism of equilibrium and kinetics to facilitate the synthesis reaction (forward) and to impede decomposition (reverse). A high concentration of reactants in the liquid phase also maximizes the kinetic rate of defect repairing. We demonstrated the advantages of LV method by synthesizing diverse high-quality 2D metal tellurides with controllable polymorphs, which would be challenging, if not impossible, to realize by using conventional methods due to weak metal-tellurium bonds, thermal instability and the co-existence of mixed crystalline phases. In particular, we successfully synthesized high-quality monolayer 2H MoTe2, which is only possible when Te defect level is substantially suppressed. Our approach provides a new paradigm in high-quality and large-scale materials synthesis and can be readily extended to a variety of quantum materials, potentially accelerating both research and industrial initiatives.